This invention relates to an industrial robot of the articulated type.
An example of industrial robot of the articulated type of the prior art is shown in FIGS. 1-3. The industrial robot shown is constructed such that as shown in FIGS. 1 and 3 rotational movement of a brachium drive motor 2 is converted into straight forward movement of a nut 3b in meshing engagement with a feed screw 3a to cause a brachium 1 to move in pivotal movement in the directions of arrows in FIG. 1 through link 4, and that as shown in FIGS. 2 and 3 rotational movement of a forearm drive motor 6 is converted into straightforward movement of a nut 7b in meshing engagement with a feed screw 7a to cause a forearm 5 to move in pivotal movement in the directions of arrows in FIG. 2 through a rod 8.
FIG. 4 shows a wrist drive mechanism of the industrial robot of the articulated type of the prior art comprising a wrist drive motor 9 (see FIG. 3) mounted in the center of pivotal movement of the brachium 1 and including an output shaft connected to a disk 11 to move the latter in swinging movement. Swinging movement of the disk 11 is transmitted through links 14 and 15 to another disk 12 to cause the latter to move in swinging movement and to cause another disk 13 to also move in swinging movement through links 16 and 17, to thereby move a wrist 18 vertically in pivotal movement. The links 14 and 15 and the disks 11 and 12 constitute a linkage of the parallelogram shape, and the links 16 and 17 and the disks 12 and 13 constitute another linkage of the parallelogram shape. Thus the wrist 18 can have its posture kept constant irrespective of the postures of the brachium 1 and the forearm 5.
Some disadvantages are associated with the industrial robot of the articulated type of the prior are described hereinabove. More specifically, since rotational movement of a drive motor is converted into straightforward movement of a nut meshing with a feed screw, the angle of rotation of the drive motor would fail to be proportional to the angle of pivotal movement of the brachium or forearm, thereby complicating calculation of the coordinates. A mechanism using a feed screw would have a shorter service life than a mechanism relying only on roller bearings for transmission of movement because wear would soon be caused on the feed screw.